The present invention relates to an improved nebulizer apparatus. Nebulizers, or atomizers, are devices that generate a fine spray or aerosol, usually of liquid. A particularly useful application for nebulizers is to provide a fine spray containing a dissolved or a suspended particulate or colloidal pharmaceutical agent for administration to a subject by inhalation. Such inhalation treatment is highly effective for conditions affecting the subject""s respiratory organs. Further, since the lungs are close to the heart and the blood circulatory system of the body, drug administration by inhalation provides an effective and rapid delivery system to all organs of the body.
In many cases, the nebulizer is placed directly in the mouth or nose of the subject so that the spray can be entrained in the respiratory gases inhaled during normal, spontaneous breathing of the subject. In other cases, the subject breathes with the aid of a respiratory ventilator. A typical ventilator has a breathing circuit comprising an inhalation limb and an exhalation limb connected to two arms of an Y-connector. The third arm of the Y-connector is connected, via a patient limb, to a mouthpiece, mask or endotracheal tube for the subject. The ventilator provides a complete or partial supply of respiratory gases to the subject through the inhalation limb during inhalation. The contraction of the subject""s lungs discharges gas through the exhalation limb during exhalation. When a nebulizer is employed in conjunction with a ventilator, it is typically placed in the patient limb.
Nebulizers currently in use for ventilator applications generate the spray either pneumatically or by means of ultrasonic vibrations. Pneumatic nebulizers are typically used with a liquid, such as an aqueous drug solution. High pressure driving gas is conducted through a nozzle to draw the drug from a drug supply for the nebulizer. The drug is discharged against a baffle or other means in a gas space of the nebulizer, breaking the liquid into a fine spray. The gas space is in fluid communication with the inhaled gas pathway of the breathing circuit so that the gas flow expelled from the nozzle along with the nebulized drug is conducted to the breathing circuit and ultimately to the subject.
Disadvantages in the use of pneumatic nebulizers include the following. If the nebulizer adds a significant quantity of gas, for example, up to five liters/minute, into the breathing circuit, the breathing gas composition is affected. The driving gas is most often either oxygen or air and, particularly when a ventilator is used in the treatment of a child, the gas flow from the nebulizer may form a major portion of the inhalation gas flow. Because of the gas flow from the nebulizer, control over the inhalation gas composition is lost. Also, due to passage of the driving gas through the nozzle, impingement of the drug on the baffle, etc., pneumatic nebulizers are noisy. This may contribute to the discomfort of the subject. And, as controlling the commencing and stopping of a drug agent spray is difficult and is not very accurate, pneumatic nebulizers are commonly active during both inhalation and exhalation. This obviously decreases the efficiency of drug delivery as measured by ratio of the amount of drug supplied to the nebulizer and the amount of drug actually delivered into the subject""s air ways.
In an ultrasonic nebulizer, the fine spray is produced by ultrasonic vibration of the liquid, as by a piezoelectric crystal. The liquid is dropped on, or otherwise applied to, the crystal. The on-off operation of such nebulizers is easier to control than for a pneumatic nebulizer. However, prior art ultrasonic devices require a large electrical power consumption to power the crystal and may not be able to nebulize colloidal or particulate suspensions. Partly due to the high power consumption of ultrasonic nebulizers, the equipment tends to be bulky. This can cause considerable difficulties, given the crowded environment that may surround a subject, such as a critical care patient.
U.S. Pat. No. 5,443,059, shows an attempt to solve the problem of bulkiness in an ultrasonic nebulizer. In the ""059 patent, a liquid source and metering component are provided in separate control units that can be located at a distance from the subject. The control unit meters liquid through a feed line to a piezoelectric ceramic plate positioned in the patient limb of the breathing circuit. The piezoelectric ceramic plate nebulizes the liquid. In the event more liquid is delivered than can be nebulized, the device is equipped with a collection vessel for the excess liquid. In the structure disclosed in this patent, the metering line for the liquid to be nebulized is located above the vibrating crystal so that the liquid drops onto the crystal. However, this renders the ultrasonic nebulizer of this patent position sensitive. Additionally, during inhalation, the flow speed of the respiratory gases can exceed 10 m/s. Such a flow speed can draw the droplets of liquid away into the respiratory gases without the droplets being applied to the vibrating crystal for nebulization. This may render the inhalation therapy less effective, or may alter dosage rates, both of which can adversely affect the subject.
U.S. Pat. No. 3,812,854 describes a nebulizer for inhalation therapy in which the spray is generated on the front surface of a vibrating, porous body. The pores of the body form a network of passages that enable the liquid to flow through the body. The liquid to be nebulized is supplied under pressure from a liquid supply through a liquid conduit to the pores, and forced through the pores to the front surface of the porous body where it is discharged as a spray.
However, the complicated flow paths in the porous body increase the flow resistance so that high liquid pressure is required to transport the liquid through the body. To resist the forces resulting from the high liquid pressure, a thick porous body is required. But, such thickness increases the weight of the nebulizer as well as the amount of electric power required to vibrate it. Also, when used with suspensions containing suspended particulate or colloidal particles, the particles may be entrapped in the complicated flow paths through the porous body.
U.S. Pat. No. 5,487,378 describes a nebulizer in which the aerosol is formed using a mesh plate instead of a porous solid body, thereby to lessen or eliminate the foregoing shortcomings. The mesh plate has a plurality of orifices for the liquid in a reservoir. The orifices are tapered outwardly toward the outlet for the liquid. The liquid or the nozzle assembly is vibrated ultrasonically by a piezoelectric element to nebulize the liquid. The liquid reservoir is preferably permanently filled with liquid and maintained at a slight negative pressure.
A specific difficulty with nebulizers based on technology where the liquid or the nozzle assembly is vibrated ultrasonically by a piezoelectric element to nebulize the liquid is the nonlinear mechanical functioning of the piezoelectric element against the electrical signal frequency driving it. The mechanical movement of the piezoelectric element may be tens or hundreds times higher at a mechanical resonance frequency compared to movement outside the mechanical resonance frequency. Because of this dramatic increase in the mechanical movement at the mechanical resonance frequency, it is much more efficient to produce the vibrations to nebulize liquid at the mechanical frequency.
U.S. Pat. No. 5, 518,179 describes a nebulizer in which the aerosol is formed using a mesh plate vibrated by a piezoelectric element that has a thin-walled structure and is arranged to operate in a bending mode. The piezoelectric element has two separate, independent electrodes: a drive electrode and a sense electrode. In operation, the drive electrode is driven by an electrical signal source at an actuator mechanical resonance. While operating at this mechanical resonance, the signal from the sense electrode has a local maximum and the drive circuitry ensures that the piezoelectric element is driven close to the mechanical resonance with a phase angle between the drive and sense electrodes.
An object of the present invention is to provide an improved nebulizer apparatus of the mesh plate type that efficiently transforms the liquid into an aerosol, but this invention can also be extended to other type of nebulizers which are run by vibrating means including a piezoelectric actuator. Another object of the invention is to provide such an apparatus that it can be easily adjusted to function at the most efficient operating point to nebulize liquid.
Furthermore, another object of the invention is to provide such an apparatus such that the state of operation for the nebulizer can be easily clarified by examining the operating point at which the vibration is produced most efficiently. By examining the state of operation, fracture of the vibrating component can be predicted and verified. By examining the state of operation, it is also possible to examine and to examine and distinguish all the broken vibrating components within the manufactured lot.
The above objects are attained by a nebulizer having vibrating means comprising a piezoelectric actuator having one or more electrode on it""s surfaces or a piezoelectric vibrator having one or more electrodes on it""s surfaces connected to a mechanical construction. The nebulizer further includes a frequency power service for exiting vibrator, a connecting means for connecting frequency power service to electrodes of the vibrator, and means for detecting the intensity of vibration produced by vibrating means.